Missing Punctuation with polymer plates

I work on an Improved Pearl with a Boxcar Base and Deep Relief plates and lately, at least more than is usually the case, punctuation marks aren’t inking. I have on one occasion needed a plate re-processed because the punctuation was clearly absent on the proof, but last night, for instance, was working on some reply cards that included two lines of text at top and bottom and an area in the middle with an m followed by a line of dots. Not small dots but not huge ones either.
Things were going along fine for the first 50 or so and then all of a sudden I could not for the life of me get the rollers to ink a few dots to the right of the m, so they weren’t at the margins of the plate, and all surrounding text was inking perfectly. It is maddening! Especially when it’s the second color I’m printing, and now have to go back and reprint the first to compensate for all of the cards with missing punctuation.
I’m not using a ton of packing or smashing the plate, and my rollers are relatively new with no flat spots, holes, etc.
Has anyone else had a problem with this? Can you offer any suggestions as to what may be going on if it is a problem with my press? I tend to think it’s the plate but really can’t be sure.
Thanks!

I don’t think your press is to blame for the problems that you’re experiencing. Under heavy impression, sometimes dots on the KF152 plates tend to drop out. This is true of all photopolymer plates but tends to happen more on the thicker plates. Here’s how we deal with it:
- If we’re on press and this happens, we add tape behind the punctuation that has worn down. Because the plate is transparent, this is easy to line up. Cut a piece of scotch tape to fit and position it with an exacto on the adhesive behind the affected area. You don’t need to remove the plate from register, just peel up the plate from the side to expose the part that needs correction. I realize this solution is not ideal, but it will help you complete the run without re-plating.
- Use soft packing and/or paper. Soft cotton paper works best for deep impression printing because it puts less stress on your plate. Soft packing helps for the same reason. We use cotton blotter paper as packing in our presses to serve as a counter and absorb the plate’s impression. The blotter needs replacing (or at least repositioning) every run.
- Consider a thinner plate. Our 94FL and KF95 plates have less polymer on their surface, so there’s less to wear down. Under heavy impression, these plates will tend to last longer. We’re able to handle deep-impression printing with the KF95 plates in our own shop. It helps to have adjustable roller rails (such as on the Heidelberg Windmill presses) so that the thinner relief doesn’t cause inking problems.
- Add a stroke to thin artwork or dots before making your plate. When we notice punctuation or a dot that we feel is going to be problematic, we often apply a 0.1 pt stroke before outputting films. This helps gives a better foundation to these areas. It’s a thin enough stroke not to be noticeable on the printed piece.
I hope these ideas help you resolve this issue! Sorry that there’s no simple solution, but with a combination of the techniques here I hope that you’ll be able to minimize your down-time.

If you have punctuation dropping out, you have an improperly exposed plate. No if ands or buts about this. If the relief structure is not correctly configured, yes, you will lose details.

But, photopolymer is not the end all it is made out to be. Isolated dots, as well as many other things, can be problematic, but allowances can be made. However, it is really up to the client to provide properly letterpress configured file work. Not everything that you can envision on the computer screen is going to translate well into physical form. A plate processor can only work with what they are given.

Thin plates do provide slightly better image fidelity, but I do not believe it is because thick plates wear down! The allowable thickness of letterpress formulated plates is a strict parameter, and for a reason. Relief depth and plate thickness have a very limited variable. But there is no reason why any plate with a thickness between .037 and .060 should not hold its own through the rigors of even the most demanding of press runs.

I’ll base my response on my extensive experience using photopolymer for deep impression printing, both in our own shop and in processing plates for over 700 platemaking customers nationwide.

We see this issue on plates in our shop regardless of exposure time. Some dots or lines are simply too small to develop the foundation necessary to withstand repeated impression with hard packing.

To get technical, the issue is not wearing down of the plates, but compression of the polymer caused by a weak foundation. After several hard hits, small dots don’t rebound quite as well—they stay down, slightly below type high. This only affects small dots, and I’ve mentioned ways (see above) to address this during pre-press and during printing.

We always work closely with our customers to ensure they’re happy with their plates. We guarantee the quality of our processing.

From your posts here I am wondering if you are suggesting that “deep relief” plates aren’t exactly suitable for “deep impression”? Could this be a matter of their backing?

I ask because I supply a KM152 steel-backed plate to several clients, who favor a deeper impression, and the loss of small dots has not been brought up as a problem.

I’m not sure that it’s a situation that small dots don’t “rebound” so much as that they might collapse from weak relief structure. The more isolated they are in terms of surface proximately, the more likely the occurrence.

For deep impression printing, yes, I actually prefer the thinner plates. The 0.027” relief of the 94FL/KF95 is more than adequate for deep impression printing, in my opinion. We offer the Deep Relief KF152 plates primarily to make inking easier on platen presses without adjustable rollers rails.

I’ve tried the KM152 plates and I find they’re very similar (if not identical) in exposure to the KF152. They experience the same problems. I’ve worked with Toyobo to minimize this issue, but they’ve been unable to help me eliminate weak dots entirely. Why? Because some dots are simply too small to hold, regardless of exposure time.

It’s late and I’m having trouble putting this process in words. Let me explain this issue with a visual aid: http://www.boxcarpress.com/flywheel/misc/dots.pdf
The middle example shows what happens when a dot is borderline between holding and washing off. This dot starts off printing okay but, because it’s weak at its foundation, doesn’t hold up well to repeated impression. Longer exposure bloats the shoulder of the dot, but doesn’t help because it still cannot harden the dot’s foundation significantly. The aperture of the dot in the film is just too small to allow enough light to reach the plate backing.

From this example, you can see how a thinner plate will always have a stronger foundation. The plate backing is much closer to the aperture of the dot in the film negative, and hardens much more easily.

Again, I want to stress that with the proper preparation of files this issue won’t happen.

That PDF is quite funny. How true. I’m wondering though how much this has to do with washout rather than inability of UV to reach the floor of the plate. Why would anyone offer a thickness of plate that is actually not functional for letterpress? Not trying to be argumentative, just the eternal search for verisimilitude. Doesn’t make sense to me.

I don’t do “deep impression” in my own work so really would not know the peculiarities. In practice I do often warn clients if I think a typeface won’t reproduce well or if isolated elements could cause problems, how to deal with solids, and whatever. Mainly, however, their concern seems to be that they want it today.

Glad you found the illustration funny! I made it to show how this is strictly an exposure (as opposed to washout) issue, but it sounds like you’re not convinced. I could go on but it really doesn’t matter. Some dots are just too small, I’m sure you’ll agree.

The plates we’re talking about ARE made for letterpress, however some dots are just too small to develop a good foundation. This problem occurs on all plates: each plate has a minimum dot that it will consistently hold. This limitation is most noticeable on thicker plates because their foundation is farther from the film.

Did I just see you equate “functional for deep impression letterpress” with “functional for letterpress”? Hehehe! Well, we all know that these plates are made for:http://www.labelmen.com/newedition5/products/images/PW-260-R6C_jpg.gif
We’re doing pretty well with our old cast iron, though. I think polymer plates are well suited to our purpose, which isn’t to say that they don’t have any limitations.

No I don’t think you “saw” me make that equation. Like I said, I have not heard this explanation for missing details on thicker plates before. There is only a difference of .022 +/- between a “thick” plate and a “thin” plate. Exposure times and washout times are different for each because of this.

If so called “deep impression” is going beyond the tolerance of the thicker plates I’d think the recommendation would be for copper dies, which do not share this problem.

I guess there is no one solution that fits each project. Intelligent counseling of the client and understanding your presses and plates capabilities goes a long way to avoiding problems.

If you are in a rush, the cost difference between copper from MM and BC photo-polymer seems to be minimal due to the shipping costs.

Still, nothing beats being able to gang up a bunch of forms on one photo-polymer sheet and being able to trim them with a blade. Multicolor jobs output as a single color photo-polymer plate. Mmmm tasty and quick makeready.

I referred to make ready as the whole process of readying the press to print. I will try to be more accurate in my language in the future.

When using polyester backed photo-polymer plates I have found it very easy to get the press set up to print. The grids on a Boxcar base help me tremendously. When I have had a multi color job where there has been enough room between the colors (1/16 - 1/8 inch) I have been able to have one plate made and then just cut out the additional colors. After the first pass I replace the removed elements and then remove the first color. Very quick set up for the next color. I have not been able to do this with copper since the kerf of the band saw blade removes too much material.

I have not yet tried the steel backed polymer plates. The bases we ordered are for the deep relief plates. I think we could get some shim stock or plate to make up for the difference in depth.

I was not sure if I should specifically use vendor names in these discussions so I used MM for Metal Magic in Arizona and BC for Boxcar in Syracuse. Both Companies offer excellent service with plates the next day if you send them files by 12:00pm or so EST. Metal Magic seems to have a better shipping cost via FedEx than Boxcar does with UPS. The difference in shipping comes close to canceling out the increased cost of copper.

The make ready seems to be the same for either plate type. This does change dramatically if a double or triple feed happens and the fine details of the polymer plates get compressed.

I will be more careful before jumping into a discussion again with the big dogs!

This has been an interesting discussion to follow over the last couple of weeks, and could not have come at a more opportune time for us in our press room.
We recently ran a job of letterhead and biz cards for a client that was designed exclusively in very small, very fine, minimal type. Can’t recall the exact type face, but everything was very slim and very delicate.
The client was very specific about everything looking sharp and clean, and we were happy to accomodate.
I had sometimes noticed small punctuation falling out on me in the past, but could always get around it using the technique Harold reccomends, with tape on the back of the plate.
This time alot of things started to go. We run film-backed photopolymer, usually from Anderson Vreeland, and after about 30 prints we noticed not just dots and commas vanishing, but letters like L and F began to lean or bow ever so slightly.
This is something i have seen that usually happens in tandem with the missing punctuation, and i assume the reasons are the same.
To make my already long story short, we reprocessed the plates a number of times, with different exposure times, etc., and processed on both Boxcar plates (kf95), as well as the Anderson Vreeland material (comparable to the kf95), and also used softer packing etc., but each time the type would slowly lose its structure.
Finally we dug out some long buried steel backed plates from way back when, and gave it a shot. They held up beautifully. Something about the structure of the steel back allowed the type to hold for over 2000 impressions, where as the film back went out after 30-40.
I routinely referenced this blog, and appreciated the lengthy discussions on precisely the trouble i was dealing with.
In the end the steel backed saved us, but overall i love the boxcar system (vs. a mag base), i suppose each material has its own subtle advantages and threshholds.
Thanks for the informative discussion guys!
-Natron

Thanks for the info. I was wondering that myself since none of my clients have seemingly experienced this with the KM152. I did bring it up but Harold dismissed it so it went no farther.

I’ve never used the thicker plates but have used the thin steel backed plates on both the Bunting and Patmag and have not experienced this problem. But I also supply the thin polyester-backed plates to clients and none of them have brought it up.

So I’m not sure your solution is necessarily the solution. One thing you mention is that the steel-backed plates were from way back when. I’m guessing they had become quite brittle, and their lack of resilience might actually be what saved the day for you. Perhaps that is a clue or sorts. It might be worthwhile running the post-exposure for a longer time to ensure curing through the photopolymer. Normally it would be 1x or 2x the initial exposure (I run 2x). Perhaps even longer?

Updated. Gerald,
When we experimented re-processing the film backed plates, it did occur to me that they might benefit from a longer post exposure process, so i doubled the amount of post exposure time. It did not seem to make a signifigant difference once on press. We also were increasing the primary exposure by about 30 seconds ontop of our standard time, and that combined with the double post exposure still did not do the trick.
We stopped using the steel backed system about a year and a half ago, in favor of the Boxcar system, so the plates we eventually used were at least that old.
We used one of our old Patmag bases. Perhaps the plate was able to hold up longer in part by the softer nature of the magnetic base surface, combined with the stiffer nature of the plate itself, as opposed to the super firm Boxcar base.
I do remember that i never noticed this particular problem in all the time we ran on steel backed plates (although we encountered alot of other little annoyances that eventually led us to switch).
I spent some time looking at the plates themselves, and i have to say that the shoulder of the type on the steel backed plate seemed a bit broader than what i could see on the film backed plates. This is just from my naked eye observation, but it appears so. It makes me wonder if the light is absorbed and distributed differently when it hits the metal backing as opposed to when it hits the transparent film, causing potential differences in the final nature of the finished photopolymer? Who knows.
Anyway, i will continue to keep an eye on our plates as we run jobs in the future, and i will keep an eye on the blog for any solutions that people are able to discover.

I was wondering about the reflective nature of the steel-backs and if that might contribute to a more complete exposure. And the Patmag as well since the softer magback seems to absorb the shock of impression and bounce back. I had a client come in a long while back and insist on deep impression on paper she was supplying. Simply did not work on the paper but I was surprised to notice that the back of the plate had significant impression marking.

One thing about the KF152s. I had inquired of my sales rep about them (in 12 years he has never steered me wrong) and he simply said no, they were not for letterpress, and mentioned embossing and moulding processes. When I asked about deep impression he said use the thinner plates since the relief difference between thin plates and thick plates was not significant enough to matter.

Back in the dark ages (1974) when I first used photopolymer plates, we used a back exposure to build the “floor” of the plate. I wonder if this provided exposed polymer at the base of the plate which might give a better overall bond of the small details to the plate?

As I remember it, it was a very short exposure through the clear base of the plate material. After washout, there was a layer of polymer material across the entire bottom of the plate.

Not possible with metal-backed plate materials, but certainly something one could try if losing detail is a concern.

It is my understanding that most, if not all, of the sheet photopolymer available today is already back exposed by the manufacturer, which is why the washout leaves a thin layer of photopolymer on the floor of the plate—on both steel-backed and polyester-backed plates.

I love this discussion. While I have never had detail drop on any of my deep relief plates from Boxcar regardless of the size, large or small, I now will keep a sharp eye out for it just in case.

I think my saving grace has been runs that do not exceed 750 quantity.

I have done work on my C&P where I just kiss the paper and where I have had to use a soft packing to get the necessary impression that the client wanted. I usually hadnset type for the “light touch” but when the paper needs impression I always have a plate made!

I have had this problem as well. As I create my oun art, I can avoid those fonts and line weights that cause problems. Actually I thought it was my plate making proceedure - by hand. I have found that unless the plate is too large my plates are fairly consistant. Exposure adjustments have not shown much improvement, nor has water temperature.
If I just stay away from hairlines, leader dots, and cursive fonts with really fine swashes things usually work just fine.